Centraliser segment and centraliser

ABSTRACT

A centraliser segment ( 11 ) which can, by itself or in combination with one or more corresponding centraliser segments, be used to form a centraliser ( 13 ) which can in use be clampingly engaged around an element ( 10 ) which is receivable in a borehole, said centraliser segment comprising a first collar portion ( 15 ), a second collar portion ( 17 ) and at least one bow element ( 19 ) extending between said first collar portion and said second collar portion to maintain the collar portions in spaced relation to each other, wherein the collars have an inner face which in use is to bear against the element and wherein said bow element has a curvature along its length to define an intermediate portion which extends laterally from the centraliser segment away from the inner faces of the collars, at least the intermediate portion of the bow elements having a convex transverse profile, a first connection element ( 21 ) provided at one end of the collar portions and second connection element ( 23 ) provided at the other end of the collar portions, wherein in use said first connection element are engagable with said second connection element of the same or another centraliser segment such that one or more said centraliser segments are connectable together to form a centraliser which in use is capable of being received around the element whereby the intermediate portions are radially outermost, said first and second connection element having an adjustment means which can cause the diameter of the centraliser to be varied.

RELATED APPLICATIONS

This application is a continuation-in-part of PCT/AU2009/000268 filed onMar. 5, 2009, which claims priority to Australian patent applicationnumber 2008901065 filed on Mar. 5, 2008. The contents of each of theseapplications is incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a centraliser segment and a centraliserformed of one or more of such centraliser segments. The centraliser canbe used with items to be located within a borehole such as rock boltsand soil nails.

BACKGROUND

One application of the centraliser is to centralise a rock bolt. Acentraliser which has been previously proposed by the inventor and whichcould be used to centralise borehole casings and rock bolts is disclosedin AU200143778. The centraliser elements of the above patentspecification incorporated a connection element which required the useof a specialised tool in causing the movement between the connectionelement when closing the interconnected ends of the centraliser to causeit to clamp around the casing or borehole. In addition the connectionelements were generally planar and were bent to be received about thecasing or rock bolt and as result their natural resilience tended toresist any tightening of the centraliser especially when being appliedaround elements of small diameter. While the centraliser elements of theform referred to above can be very advantageous when used with pipes orcasings they present problems when applied to elements of smallerdiameter such as rock bolts and soil nails

The discussion throughout this specification, of the background andprior art to the invention is intended only to facilitate anunderstanding of the present invention. It should be appreciated thatthe discussion is not an acknowledgement or admission that any of thematerial referred to was part of the common general knowledge inAustralia and the world as at the priority date of the application.

DISCLOSURE OF THE INVENTION

Throughout the specification and claim, unless the context requiresotherwise, the word “comprise” or variations such as “comprises” or“comprising”, will be understood to imply the inclusion of a statedinteger or group of integers but not the exclusion of any other integeror group of integers.

In accordance with one aspect of the present invention, there isprovided a centraliser segment which can, by itself or in combinationwith one or more corresponding centraliser segments, be used to form acentraliser which can in use be clampingly engaged around an elementwhich is receivable in a borehole, said centraliser segment comprising afirst collar portion, a second collar portion and at least one straplike resiliently flexible bow element extending between said firstcollar portion and said second collar portion to maintain the collarportions in spaced relation to each other, wherein the collars have aninner face which in use is to bear against the element and wherein saidat least one bow element has a curvature along its length to define anintermediate portion which extends laterally from the centralisersegment away from the inner faces of the collars, said bow elementsbeing resiliently flexible and each bow element having a convextransverse profile and having a varied width along their length which isgreatest at the central intermediate portion, a first connection elementprovided at one end of the collar portions and second connection elementprovided at the other end of the collar portions, wherein in use saidfirst connection element are engagable with said second connectionelement of the same or another centraliser segment such that one or moresaid centraliser segments are connectable together to form a centraliserwhich in use is capable of being received around the element whereby theintermediate portions are radially outermost, said first and secondconnection element having an adjustment means which can cause thediameter of the centraliser to be varied.

According to a preferred feature of the invention each bow element isconfigured to have a curvature along its length

According to a preferred feature of the invention wherein the collarportions are curved along their longitudinal axis to have a curvaturewhich at most approaches the curvature of the element to which thecentraliser is to be applied.

According to a preferred feature of the invention the first connectionelement comprises a passage formed along the respective collar portionto extend inwardly from the respective end and the second connectionelement comprises an elongate element which in use is able to bereceived in the passage, the elongate element formed with a set ofserrations spaced along at least a portion of its length, the passageformed with a pawl element which is positioned to resiliently engage theserrations to control the longitudinal movement of the elongate portionwhen received in the passage. According to a preferred feature of theinvention the engagement of the pawl member with the serrations is suchas to permit the reduction in diameter of the centraliser but to resistan increase in the diameter of the centraliser. According to a preferredfeature of the invention the outer face of the collar is provided with apair of transversely spaced retention lugs located in spacedrelationship from the passage, the retention lugs configured andarranged to receive the portion of the elongate element passing from thepassage on application of the centraliser to the element to hold theportion in close abutting relationship with the outer face of thecollar. According to a preferred feature of the invention a plurality ofpairs of retention lugs are provided.

According to a preferred feature of the invention at least two bowelements extend between said first and second collar portions.

According to a preferred feature of the invention, said first and secondcollar portions are substantially parallel.

According to a preferred feature of the invention said first and secondcollar portions are provided as strap-like members.

According to a preferred feature of the invention said centralisersegment is made of a corrosion resistant material.

According to a preferred feature of the invention the inner face of thecollars between the connection element is provided with a protrusion atspaced intervals along the length of the collars. According to apreferred feature of the invention the protrusions comprise a rib-likeformation extending transversely across the inner face of the collars.

In accordance with a second aspect of the present invention, there isprovided a centraliser for an element comprising a centraliser segment,as hereinbefore described, wherein the ends of one or more centralisersegments are connected together via said first and second connectionelement around the element to provide a centraliser for the element.

The invention will be more fully understood in the light or thefollowing description of one specific embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The description is made with reference to the accompanying drawings, inwhich:

FIG. 1 is an isometric view of a centraliser segment according to thefirst embodiment;

FIG. 2 is a side elevation of a centraliser segment according to thefirst embodiment.

FIG. 3 is an end elevation of two centraliser segments according to thefirst embodiment joined together to form a centraliser;

FIG. 4 is an isometric view of the centraliser showing the inner face ofthe centraliser segment; and

FIG. 5 is an illustrative view of a centraliser according to the firstembodiment in position around a rock bolt which is in position within abore hole.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENT

The embodiment comprises a centraliser segment 11 which is intended inuse to be used by itself or in combination with other correspondingcentraliser segments to form a centraliser 13 which can be applied to arock bolt 10 as shown at FIG. 4 whereby the ends of a single segment ora set of interconnected segments are connected together to form anannular centraliser 13 which in use is to located around the rock bolt10 to centralise the rock bolt 10 within a borehole. The use of a set ofinterconnected segments to form a centraliser 13 is required with rockbolts 10 having medium to large diameters, whilst the use of a singlesegment to form the centraliser 13 of is appropriate with rock bolts 10having small diameters. The centralisers 13 are formed of a suitableplastics material which is resistant to corrosion and has sufficientrigidity and resilience to perform its function as a centraliser.

The centraliser segment 11 according to the embodiment comprises a firstcollar portion 15 and a second collar portion 17 which are held inspaced parallel relationship by a set of substantially parallel bowelements 19, which extend between the first and second collar portions15 and 17. The first and second collar portions 15 and 17 are curvedalong their length.

The bow elements 19 are strap-like members which are curved along theirlength such that the central intermediate portion of the bow elements 19extends laterally to one side of the centraliser segment. When thecentraliser 13 is mounted to the rock bolt 10 (as shown at FIG. 4) thecollar portions 15 and 17 snugly engage the rock bolt 10 while the bowelements 19 extend outwardly from the side of the rock bolt 10 to locatethe rock bolt 10 centrally within the bore hole. In addition the bowelements have a varied width along their length which is greatest at thecentral intermediate portion. In addition each bow element has a convextransverse external profile.

Each end of each collar portion is provided with connector element 21and 23 where the connector elements on each collar are the same and theconnector elements on each collar are complementary to each other andenable the ends of a centraliser element or of another correspondingcentraliser element to be lockingly interconnected as shown at FIG. 3 todefine a centraliser 13. In addition once the connector elements areinter-engaged to form a centraliser 13 the diameter of the resultantcentraliser 13 is able to be varied.

The first connector elements 21 which are provided at one end of bothcollar portions comprises a longitudinally directed passage 25 which isformed on the outer face of the collar. The interior of the passage isprovided with a pawl (not shown). The second connector elements 23 areformed as tongue-like extensions of the collar and are dimensioned andconfigured to be slidably receivable in the passage 25 of the firstconnector elements. The passage is of similar cross section to thetongue-like extensions. The outer face of the extensions are formed witha set of serrations 27. When the extension of the second connector isreceived in the passage 25 of the respective first connector the pawlwithin the respective passageway will engage with the serrations 27 toretain the extension within the passage. The nature of the engagement issuch that the extensions can move within the respective passage toreduce the diameter of the centraliser but cannot move such as toincrease the diameter of the centraliser. Each passage 25 is associatedwith pairs of retention lugs 31 which are located at spaced internalsform the inner axial end of the respective passage. Each of theretention lugs are formed at their outer ends with a flange likeextension where the portions of each pair of lugs are in opposedrelation to each other. The spacing between each pair of lugs and thespacing of their flange-like extensions is such that the lugs willreceive and retain the portion of the ends of the second connectorelements after they have passed through the passage.

The free ends of the single centraliser segment or of a set ofinterconnected centraliser segments are interconnected to form acentraliser 13. In the case of small diameter rock bolt 10, a singlecentraliser segment can be used and in the case of larger diameter rockbolt 10 two or more centraliser segments 11 are able to be connectedtogether end to end via the first and second connectors 21 and 23. Theinterconnection between the ends is effected by inserting the extensionsof the second connectors into the passage 25 of the respective firstconnectors until the serrations 27 on the second connectors are engagedby the pawl and as a result the further movement of the extension withinthe passage is controlled by the pawl. The diameter of the centraliser13 is able to be adjusted through a range which is determined by thelength of the serrated portion 27 of the extensions.

In addition as shown at FIGS. 3 and 4 the inner face of each collar isprovided with a set of protrusions or fillets 29 at spaced intervalsalong the collar. Each of the protrusions or fillets comprises a rib andwhich is located centrally across the width of the inner face of thecollar to extend transversely across the inner face of the collar.

In use the centraliser 13 is fixed around the rock bolt 10 prior to therock bolt 10 being inserted into a borehole. The amount of longitudinalcurvature in the bow elements 19 of the centraliser segments forming acentraliser 13 can be varied to accommodate for the clearance betweenthe borehole 10 and the rock bolt 10. This can be done by first affixingone collar of the centraliser 13 around the rock bolt 10 and tighteningit around the rock bolt 10. If an increased curvature is required in thebow elements 19 then the other collar is located around the rock bolt 10and is pushed in the direction of the one collar and then it is firmlyclamped around the rock bolt 10. Pushing the collar portions togetherwill increase the curvature of the bow elements 19. Alternativelypulling the collar portions away from each other will lessen thecurvature of the bow elements 19.

Due to the bow elements 19 being flexibly resilient, as the rock bolt 10is pushed into the borehole, the bow elements 19 will resiliently deformif they encounter any obstruction in the wall of the borehole and oncethe bow elements 19 pass over the obstruction, they will return to theirnormal shape to maintain contact with the wall borehole. Maintaining thebow elements 19 in contact with the wall of the borehole ensures thatthe rock bolt 10 remains centralised as it is inserted into theborehole.

One advantage offered by the embodiment is that the application of thecentraliser according to the embodiment does not require the use of aspecialised tool which is the case of at least some of the embodimentsof AU200143778.

Furthermore the convex transverse external profile of the bow elementsprovides a further advantage since such curvature ensures that in theevent the centraliser is caused to rotate within the borehole as aresult of rotation of the rock bolt 10 within the borehole the convexcross section of the bows enables the lateral edges of the bow elementsto remain clear of the side walls of the borehole and will not becomeengaged with the sides of the borehole thus enabling the centraliser tomore readily rotate with the rock bolt. In action the curvature of thebows provides a further advantage in that it improves the strength ofthe bows when compared with the bows of AU200143778.

Furthermore the feature of the bow elements having a variable width andthat the bow elements have the greatest width intermediate their lengthprovides the following advantages:

-   -   It maximises the flexural strength of the bows, and therefore        the centralizing force that is applied to the casing or        rockbolt.    -   It increases the surface area of the portion of the bows that is        to come into contact with the borehole wall, thereby reducing        the pressure exerted by the bow on the borehole wall at the        contact point whilst maintaining the desire centralising force        which reduces the potential for the bows to track and or gouge        into softer formations.    -   The reduction in pressure also reduces wear/abrasion on the        bows.

Increasing the width of the bows along their entire length wouldinterfere with the flexibility of the collar portions, reducing therange of diameters to which the centralizer segments can be applied.

Furthermore the inherent curvature of the collars enable the centraliserto be applied around the rock bolt and whereby the degree of forcerequired to tighten the centraliser to the rock bolt is reduced. This isof significant advantage where the centraliser is used with smalldiameter rock bolts. Furthermore in the case of rock bolts having adiameter greater than the curvature of the collar portions the resultantcentraliser will be clampingly received around the rock bolt and thetightening of the connectors only serves to supplement such engagement.

A further advantage of the centraliser segment according to theembodiment is the presence of the protrusions 29 which serve to improvethe frictional engagement of the centraliser with the rock bolt toprevent longitudinal movement and angular movement of the centraliseralong and around the element respectively.

A further advantage of the centraliser segment according to theembodiment is that on interconnection of connector elements of thecollars to form a centraliser the free ends of the second connectorelements which pass from the passages of the first connector elementsare retained in snug engagement with the outer face of the collar by theretention lugs 31 and it becomes unnecessary to trim the free ends ofthe second connector elements before inserting the element into aborehole

The present invention is not to be limited in scope by the specificembodiment described herein. The embodiment is intended for the purposeof exemplification only. Functionally equivalent products, elements andmethods are clearly within the scope of the invention as describedherein In addition the invention is not limited to use with rock boltsbut can be used with any other similarly dimensioned element which is tobe located within a borehole.

1. A centraliser segment which can, by itself or in combination with oneor more corresponding centraliser segments, be used to form acentraliser which can in use be clampingly engaged around an elementwhich is receivable in a borehole, said centraliser segment comprising afirst collar portion, a second collar portion and at least onestrap-like resiliently flexible bow element extending between said firstcollar portion and said second collar portion to maintain the collarportions in spaced relation to each other, wherein the collars have aninner face which in use is to bear against the element and wherein saidbow element has a configuration such as to define an intermediateportion which extends laterally from the centraliser segment away fromthe inner faces of the collars, said bow elements having a convextransverse profile and having a varied width along their length which isgreatest at the intermediate portion, a first connection elementprovided at one end of the collar portions and a second connectionelement provided at the other end of the collar portions, wherein in usesaid first connection element are engagable with said second connectionelement of the same or another centraliser segment such that one or moresaid centraliser segments are connectable together to form a centraliserwhich in use is capable of being received around the element at whichposition the intermediate portions are radially outermost, said firstand second connection element having an adjustment means which can causethe diameter of the centraliser to be varied.
 2. A centraliser segmentas claimed at claim 1 wherein each bow element is configured to have acurvature along its length.
 3. A centraliser segment as claimed at claim1 wherein the collar portions are curved along their longitudinal axisto have a curvature which at most approaches the curvature of theelement to which the centraliser is to be applied.
 4. A centralisersegment as claimed at claim 1 wherein the first connection elementcomprises a passage formed along the respective collar portion to extendinwardly from the respective end and the second connection elementcomprises an elongate element which in use is able to be received in thepassage, the elongate element formed with a set of serrations spacedalong at least a portion of its length, the passage associated with apawl element which is positioned to resiliently engage the serrations tocontrol the longitudinal movement of the elongate portion when receivedin the passage.
 5. A centraliser segment as claimed at claim 4 whereinthe engagement of the pawl member with the serrations is such as topermit relative movement between the pawl and the passage to cause areduction in diameter of the centraliser but to resist an increase inthe diameter of the centraliser.
 6. A centraliser segment as claimed atclaim 4 wherein outer face of the collar is provided with a pair oftransversely spaced retention lugs located in spaced relationship fromthe passage, the retention lugs configured and arranged to receive theportion of the elongate element passing from the passage on applicationof the centraliser to the element to hold the portion in close abuttingrelationship with the outer face of the collar.
 7. A centraliser segmentas claimed at claim 6 wherein a plurality of pairs of retention lugs areprovided.
 8. A centraliser segment as claimed at claim 1 wherein atleast two bow elements extend between said first and second collarportions.
 9. A centraliser segment as claimed claim 1 wherein said firstand second collar portions are substantially parallel.
 10. A centralisersegment as claimed at claim 1 wherein said first and second collarportions are provided as strap-like members.
 11. A centraliser segmentas claimed claim 1 wherein said centraliser segment is made of acorrosion resistant material.
 12. A centraliser segment as claimed atclaim 1 wherein the inner face of the collars between the connectionelement is provided with a protrusion at spaced intervals along thelength of the collars.
 13. A centraliser segment as claimed at claim 12wherein the protrusions comprise a rib-like formation extendingtransversely across the inner face of the collars.
 14. A centraliser foran element comprising a centraliser segment of the form as claimed atclaim 1 wherein the ends of one or more centraliser segments areconnected together via said first and second connection element aroundthe element to provide a centraliser for the element.